Researching pottery for a third-world setting, I found the kiln to be the trickiest point.
The clay is ‘mined’, prepared by slurry to sort off the large pieces and screened to reserve only the clay, and then sand or mica or other materials are added to it. It is then dried to the consistency that we use in the classroom. Hopefully, the pottery and kiln can be built close to the source of clay.
I researched a design for a kiln dug out of a hillside, a pit kiln and a built kiln out of brick. I even found a hollow tree trunk kiln.
Hollow Tree Trunk Kiln
Richard Boyt talks about using a hollow tree stump to low-fire clay without any added insulation. It is so well insulated that the outsides never get hot, it can be picked up and put aside, then smothered or doused and used again.
http://www.bioenergylists.org/stovesdoc/Boyt/ceramics/ceramics3b.html
To quote an interesting part of the report:
“Save any char that is left. We can use it later to make a lightweight ceramic insulation. Also save ash. We can use it to make a high-potassium liquid that serves as a semi-glaze. I have used it to harden the surface of lightweight ceramic insulation.”
A little more basic kiln is the pit kiln.
Oaxacan Pit Kiln
This kiln is filled with pots and sticks of wood. The wood is just stacked around, under and over the pots very carefully. There is no chimney, and the kiln burns and smolders overnight, producing a low firing, certainly below cone 04.
I would like to try this pit kiln:
http://www.micaweb.com/purple/emine/outdoor.html
The kiln described here uses three inches (3″) of sawdust, then the rack, then your low-fire clay pieces, then sawdust. Another rack, pots, then sawdust, and so on.
I can imagine problems with getting the sawdust to burn, but wicks of brush or other material set throughout the sawdust and pots would fix that.
The pit is then covered with a lid that’s raised a few inches with bricks for ventilation. The lid used in this example is a galvanized steel trashcan lid.
I’ve seen the same thing done with dried cow patties, and I’ve also seen clay plastered on the inside to self-bake and create a more permanent pit kiln. The only ventilation this kiln needs is through the top, which simplifies the design considerably.
I found a great site for pit-fired pottery, this pit is used for decorative finishes and not always as a hardening process.
Pit fired ceramic is more porous (softer) because of the lower temperatures. 800-1200 degrees Fahrenheit is typical.
http://www.robertcomptonpottery.com/Method%20of-Pit-Firing-Pottery.htm
Carbon Trapped pit-fired pot
The most basic pit kiln I have found is on the Potters for Peace website.
Nicaragua roadside kiln
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